History

Already in the first round of the manga, Red meets Team Rocket Grunts who are after the mysterious Mew. As later revealed, Team Rocket was trying to clone Mew in order to create an even more powerful Pokémon. The first glimpse of this clone is seen in Tauros the Tyrant, when Red infiltrates Team Rocket headquarters in Celadon City, trying to find information about Green. He ends up in a secret underground laboratory, where he hears Blaine, working as a Team Rocket scientist, explaining that they need more cells to be taken from Mew to complete the clone.

Despite Red's attempts, Blaine eventually manages to create Mewtwo, but he is forced to use human cells from his own arm in addition to Mew's cells to do so. As a result of a backlash of Mewtwo's cells making way to his arm, Blaine and Mewtwo become linked, and can always track each other. Mewtwo then escapes after destroying the entire laboratory, and Blaine leaves Team Rocket to find it. After Team Rocket is finally defeated, Red meets Blaine again in the Cerulean Cave in And Mewtwo Too!?, and together they try to kill it, as with Mewtwo's power hitting it with even the Master Ball seemed impossible. After a hard battle against Mewtwo's twister Psywave, Pika manages to throw Blaine's Master Ball at the Genetic Pokémon, catching it. Red then gives Mewtwo to Blaine, and tells him to teach Mewtwo that humans are not all arrogant and cruel creatures. Afterwards, Blaine asks Red if he'd feel like having a Trainer battle sometime, to which Red obliges, but only if his injuries are healed first. Blaine notices the pain from his right arm has subsided, and deems Red a true Pokémon Trainer.

Mewtwo was next seen resting under Blaine's care in Purrrr-sian in a tank. Since Blaine finds out that being too far from Mewtwo puts a strain on Mewtwo's body due to their genetic link, Mewtwo lives in specially engineered fluid. For travel, Blaine fills Mewtwo's Master Ball with that fluid.

When Yellow later visits Cinnabar Island in Putting It On The Line... Against Arcanine, she finds Blaine and Mewtwo training together for the upcoming battle against the villainous Elite Four. Once the battle finally starts on Cerise Island, Yellow and Blaine find themselves teamed up against the powerful Lance, and Blaine uses Mewtwo against Lance's entire team in Airing Out Aerodactyl and Draggin' In Dragonair. Despite its best efforts, Mewtwo fails to defeat Lance within the three minutes it can live out of its special fluid, wasting the last of Blaine's strength on an attempt to deactivate Lance's Ultra Balls. Though it tried attacking the mastermind at first after Blaine collapsed (and Lance revealed his three remaining dragons were underground, safe from harm), knowing that further battle will kill Blaine, Mewtwo is forced to return to its Master Ball and leave Yellow on her own in Aerodactyl Redux.

A year after the events at Cerise Island, Blaine leaves Mewtwo in his laboratory as he goes to participate in the opening ceremony of the Pokémon League with the other Gym Leaders of Kanto and Johto. While there, Blaine finds the legendary Entei, who chooses the former as its partner. Entei then uses its special flames to heal Blaine's arm, effectively cutting the link between Blaine and Mewtwo. Sensing what happened, Mewtwo then leaves Cinnabar Island, a free Pokémon.

Mewtwo once again appears years later in the Sevii Islands in end of Reason to Fight where it has rescued an injured Lorelei who had lost due to Sird's trickery. In Mewtwo Participates in the Battle it invites Red to fight on his side against Team Rocket and Deoxys. Unlike previous chapters, in this chapter Mewtwo communicates directly with the other characters via telepathy, explaining that it gained the ability after going through the experience of having a master and leaving him. At first it only communicates with Red and Yellow (being the only ones who had earned his respect besides Blaine), but later it starts trusting Blue as well. Another person it manages to communicate with is Giovanni, but only for the purpose of letting him feel its fury.

Blue and Green are shocked to find out the psychic mutant who had so burdened Red in battle in the past has teamed up with them for the battle, but become even more flabbergasted they are when Mewtwo uses a mere Psywave attack that takes out all of the Unown guarding Trainer Tower with enough power to be compared to all three of their newly learned Ultimate Attacks at once. They eventually reach the top of the building where Team Rocket again show a display of their cowardly schemes by displaying holograms of the kidnapped parents of Green and Professor Oak to capture the two Trainers, whom Mewtwo then saves and states they were fools for falling for such a trick to begin with. When they enter the tower, however, things would only get worse as the Deoxys Giovanni captured has unleashed an army of clones of itself known as the Deoxys Divides, against whom the three Pallet TownPokédex holders have a hard time dealing with, and things only escalate for the worse as Giovanni also joins the fray.

Mewtwo explains to Red and Giovanni that it came to battle because it saw itself in Deoxys, the two of them having very similar species names, and wanted to keep Team Rocket from using Deoxys in the same manner they used him. Giovanni explains that Deoxys, while seemingly alike to Mewtwo, is in fact the result of an alien virus attached to the meteorite that had mutated once exposed to a strong ray, and is now his to command for good. Enraged, Mewtwo charges at Giovanni, but he slows Mewtwo down by restraining it in a special armor called "M2 Bind", which can withstand virtually all Pokémon attacks and slowly sap Mewtwo's energy. Red, Blue, and Green eventually manage to break the armor by using Saur, Charizard, and Blasty's newly learned ultimate moves, Frenzy Plant, Blast Burn, and Hydro Cannon, at the exact same time from different directions. The moves' types cancel each other out before hitting Mewtwo, thus eliminating any pain Mewtwo would feel.

Mewtwo trapped with "M2 Bind"

Free again, Mewtwo departs with Red and Charizard after Giovanni. They catch up with him in Viridian City, where Mewtwo battles under Red's command against Giovanni and Deoxys on Team Rocket's flying battle stadium. The battle proves very long and difficult for both sides, but eventually Deoxys is defeated after it loses its ability to access its Speed and Normal Formes, allowing a recovered Mewtwo to strike it with a psychic energy blast, though it fails to kill it as it was in its Defense Forme. The danger is not over, however, as Carr reveals that he planted his many Forretress all over the battleship, and they are ready to self destruct and crash the ship. To protect his friends, Red asks Deoxys to send Mewtwo and Yellow to safety via its "black hole", despite their protests.

Mewtwo eventually emerges on the other side of the black hole in front of Blue, Green, and Silver in Vermilion City, holding a sleeping Yellow. Mewtwo is too exasperated to help save Red, but is the only one to notice Mew arrive to help land the battleship safely. Realizing that it finally has someone to trace its roots back to, for he was cloned from Mew's eyelashes - Mewtwo says goodbye to Deoxys, who then flies away. Just then, Sird of Team Rocket returns and tries to recapture Deoxys with a special beam. To stop her, Mewtwo and the kids jump in front of the beam, resulting in the Pokédex holders turning to stone.

What had happened to Mewtwo at the climax of the FireRed & LeafGreen chapter was unknown until Sird's reappearance at the end of this chapter. She reveals that the reason for the Pokédex holders' petrification was because that Mewtwo had clashed with the Pokémon she was intending to use on Deoxys, Darkrai. Mewtwo was revealed to have continued chasing her after the Pokédex Holders petrification but eventually lost her.

Moves used

A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.

Trivia

Mewtwo's design, as well as its personality, have been slightly altered in the FireRed & LeafGreen chapter to give it more character. The new design resembled Mewtwo's anime counterpart, and even the armor Giovanni trapped Mewtwo in resembled the armor Mewtwo wore in the anime while under Giovanni's control.

Although Mewtwo is a genderless species, he is constantly referred to as male by other characters.